The present invention relates to semiconductor crystal growing equipments. More particularly, it relates to a vapor controlled czochralski (VCZ) single crystal growth apparatus.
In a conventional single crystal furnace for producing compound semiconductor crystals, a hot-wall sealed container is provided outside of the crucible in order to prevent decomposition loss of the compound and to assure a proper stoichiometry of the compound single crystal. This will not result in coagulation of the mixed steam evaporated from the crucible (primarily the steam of elements with high decomposition pressure) and form the mixed vapor in the container. The other hot-wall sealed containers are integral and not easy to assemble. They cannot be opened when they are hot, and cannot be used repeatedly. Therefore, they are not convenient to operate, and it increase the manufacture cost.
The object of the present invention is to provide a czochralski single crystal growth apparatus with vapor pressure control, wherein the hot-wall sealed container can be opened when it is still hot, and can be used repeatedly. Thus, it is convenient for installation and has better sealing property. It is easy to control the vapor pressure therein.
A VCZ single crystal growth apparatus of the present invention comprises a single crystal furnace, a heating unit, mechanical transmission unit and gaseous adjustment unit. In the single crystal furnace, mounted is a hot-wall sealed container. The hot-wall sealed container comprises an upper part and a lower part, and a sealing connection device between the upper and lower parts of the container. Within the hot-wall sealed container mounted is a crucible, and a crucible-transmitting shaft and a seed crystal shaft is embedded in the hot-wall sealed container through respective sealing devices.
The sealing connection device of the container is includes an annular groove. The annular groove integrates with the top of the lower part of container, and the end of the upper part of container fits within the annular groove. At the top of the hot-wall sealed container, there is an observation window.
The sealing device of the crucible-transmitting shaft and the seed crystal shaft is consisted of sealing chamber and sealing ring. The sealing chamber has an annular groove therein, and a central hole at its bottom. The sealing ring has a groove, and it is affixed with the sealing chamber so that the outer peripheral surface is fitted tightly with the inner surface of the sealing chamber. The groove of the sealing ring and the annular groove of the sealing chamber are connected face to face to form a liquid storage chamber. An interval exists between the groove of sealing ring and the upper edge of the central hole of the sealing chamber. The height of the sealing ring is smaller than the height of the annular groove of the sealing chamber.
The crucible-transmitting shaft passes through the lower end of the sealing device, a connection accepter which faces to the sealing chamber is affixed on the crucible-transmitting shaft. The sealing chamber and the sealing ring can be integrated, which includes a liquid storage chamber. The height of the sealing ring is one third to two third of the height of the annular groove of the sealing chamber.
The seed shaft is comprised of upper and lower seed shafts. The upper seed crystal shaft is solid rod while the lower seed crystal shaft is a hollow rod. The end of the upper seed shaft has a connecting shank that fits tightly with the connecting hole of the top of the lower seed crystal shaft, and a pin passes through the connecting shank and connecting hole. The end of the lower seed crystal shaft has a seed installation hole on which is a site pinhole. The connecting shank is carved with an annular groove, and the lower edge of the annular groove is tempered with conic slant.
This VCZ single crystal growth apparatus of the present invention has the following advantages:
1. The hot-wall sealed container of the apparatus has simple structure, and is easy to assemble. It can be opened when it is hot and can be used repeatedly. The hot-wall sealed container is divided into upper and lower container parts, and has a sealing connection device therebetween. An annular groove is used to seal the sealing connection device, and boron oxide is filled into the groove. At high temperature, boron oxide is melted and thus surrounds the end of the upper container part to form liquid seal. This seal has simple structure and is better in performance, and easy to install. The container can be opened when it is hot, and will not cause any damage to the upper and lower container parts. Thus, such a hot-wall sealed container may be used repeatedly. It may even reduce the operation and manufacture cost.
2. Because the seal of the hot-wall sealed container of the apparatus is good, it is easy to control the vapor pressure within the hot-wall sealed container. The sealing between the hot-wall sealed container and the seed shaft and the crucible-transmitting shaft also utilizes the sealing of the liquid boron oxide. The liquid boron oxide, after being melt, sticks on the seed shaft and the crucible-transmitting shaft such that it fills all intervals between the sealing device and the seed shaft or crucible-transmitting shaft. This prevents the mixed vapor in the hot-wall sealed container from leaking, maintains the desired vapor pressure, and facilitates the control adjustment of the vapor pressure in the hot-wall sealed container.
3. The size of the seed shaft becomes smaller, but it is better centered and has better seal. It vibrates less when it rotates so that the crystal grows better. The lower part of the seed shaft is a hollow rod with thin wall such that it deforms less when being heated. Therefore, it can be properly conjugated with the sealing device of the hot-wall sealed container to ensure the better sealing of the sealing devices. The upper and lower parts of seed shafts are fitted tightly. It can prevent the vapor in the hot-wall sealed container from leaking through the connection. The connection surfaces of the upper and lower seed shaft are accurately machined to have a precise size such that they are well centered and do not vibrate during the rotation. This benefits the crystal growth. If the seed shaft is made of ceramic material, it has better erosion resistance, and may be used longer and reduce the secondary pollution.
4. It is convenient to adjust the vapor pressure in the hot-wall sealed container, and benefits to the adjustment of the stoichiometry of the single crystal.
5. This apparatus is mainly suitable for growing GaAs, InAs and GaP crystal. The quality of this crystal is good, and the dislocation density is low. For instance, the dislocation density of the "PHgr"3xe2x80x3 semi-insulating GaAs single crystal may be 7000 cmxe2x88x922 to 9000 cmxe2x88x922, and the dislocation density of the "PHgr"4xe2x80x3 semi-insulation arsenic gallium single crystal may reach 3.5xc3x97104 cmxe2x88x922 to 4.2xc3x97104 cmxe2x88x922.